Cutting of deposit forming steel and cutting tools for such steels

ABSTRACT

CUTTING OF DEPOSIT FORMING STEELS, SUCH AS DESCRIBED IN FRENCH PAT. NO. 1,387,441, WITH TUNGSTEN CARBIDE CUTTING INSERT HAVING A HIGH TUNGSTEN CARBIDE CONTENT IS DIFFICULT. EFFICIENT CUTTING OF SUCH DEPOSIT FORMING STEELS OVER A WIDE SPEED RANGE FROM ABOUT 50 TO ABOUT 35 M./MIN. IS MADE POSSIBLE BY EMBODYING IN THE CUTTING EDGE SURFACE STRATUM OF THE CUTTING TOOL AT LEAST 15% OF ONE OR MORE OF THE CARBIDES OR BORIDES OF TI, TA, ZR, NB AND V, OR AT LEAST 50% ALUMINUM-OXIDE IN THE TOOL SURFACE STRATUM MAY BE EMBODIED EITHER BY DIFFUSION, OR BY AFFIXING SUCH SURFACE LAYER TO KNOWN TUNGSTEN CARBIDE INSERT, OR BY SINTERING STRATIFIED COMPACTS OF POWDER PARTICLE MIXTURES COHERING A THICK POWDER MIXTURE LAYER CONTAINING A LARGE PROPORTION OF TUNGSTEN CARBIDE IS COVERED ALONG ONE OR ON ITS OPPOSITE LAYER SURFACES WITH A THIN POWDER MIXTURE STRATA, EACH OF WHICH CONTAINS AT LEAST 15% OF ONE OR MORE OF THE CARBIDES OR BORIDES OF TI, TA, ZR, NB AND V.

Feb. 23, 1971 w. SCHEDLER ETAL 3,564,683

)I CUTTING OF DEPOSIT FORMING STEEL AND CUTTING l TOOLS FOB SUCH STEELS I Filed June 13. 1968 United States Patent O U.S. Cl. 29-95 2 Claims ABSTRACT F THE DISCLOSURE Cutting of deposit forming steels, such as described in French Pat. No. 1,387,441, with tungsten carbide cutting insert having a hi-gh tungsten carbide content is difficult. Efiicient cutting of such deposit forming steels over a wide speed range from about 50 to about 35 m./rnin. is made possible by embodying in the cutting edge surface stratum of the cutting tool at least of one or more of the carbides or borides of Ti, Ta, Zr, Nb and V, or at least 50% aluminum-oxide in the tool surface stratum may be embodied either by diffusion, or by affixing such surface layer to a known tungsten carbide insert, or by sintering stratified compacts of powder particle mixtures coherin-g a thick powder mixture layer containing a large proportion of tungsten carbide is covered along one or on its opposite layer surfaces with a thin powder mixture strata, each of which contains at least 15% of one or more of the carbides or borides of Ti, Ta, Zr, INb and V.

This invention relates to cutting steels which produce non-metallic deposits when being shaped by a cutting tool insert, for example, on a lathe or milling machine.

As is known, when certain types of steel, such as described in French Pat. |No. 1,387,441, When being machined or shaped by a cutting tool, the steel discharges or excretes on the surface of the tool cutting edge nonmetallic deposits which materially affect the efficiency of the cutting action. It has been proved that these nonmetallic deposits are formed by non-metallic additions or inclusions which are produced within the steel by the deoxidation treatment. By certain lknown melting and deoxidation treatments, it is possible to produce steels which may be cut to shape over a wide range of speed.

Deoxidation additions for producing steels which excrete such non-metallic content comprise alloys containing 45-90% silicon, 0.5-40% calcium, 0.5-8% manganese, up to 4% aluminum, with the balance, except for impurities, iron. When using such alloys in the steel melting there are formed glass-like inclusions having a relatively -wide melting range. Then such steel is shaped by a cutting tool. Its rising temperature softens these inclusions causing these inclusions to flow and deposit at the edge surface of the tool. As is known, the cutting tool inserts which are now Widely used for shaping steel consist of sintered carbides of tungsten, molybdenum and chromium with a binder content of one or more metals of the iron group, namely cobalt, nickel and iron. (Throughout the specification and claims, all proportions are given by weight.)

The present invention is based on the discovery that the formations of such non-metallic inclusion deposits on steel-cutting tools is determined not only by the presence of non-metallic inclusions within the steel body but also by the composition of the cutting tool or cutting tip insert. Extensive tests have confirmed that cutting tools which have high heat-strength (or strength at high temperatures) and high erosion strength are instrumental in causing the steel to excrete the non-metallic deposits on the cutting tool edge over a wide range of cutting speeds. In accordance with the invention, cutting tools having such high-heat and erosion strengths are those which contain a considerably high proporiton of the carbides, and/or borides of one or more of the metals consisting of titanium, vanadium, tantalum, zirconium and niobium, or at least 50% of aluminum oxide.

In accordance with a feature of the invention, such non-metallic inclusion containing steels are cut to desired shape with known sintered carbide tool inserts which have embodied in their cutting edge surface a sintered carbide stratum containing high proportions of the carbides or borides of one or more of the metals consisting of titanium, vanadium, tantalum or niobium or at least 50% of aluminum oxide.

The foregoing and other features of the invention will best be understood from the following more detailed description of exemplifications thereof in connection with the annexed drawings, wherein FIG. l is a graph wherein the efliciency with which a cutting tool insert of the invention removes material from a steel body containing non-metallic occlusions is compared with the cutting efficiency of heretofore used cutting tool inserts on the same steel body;

FIG. 2 is a cross-section along line 2-2 of FIG. 2a, of one example of steel-cutting tool insert of the invention;

FIG. 2a is a top view of the same tool insert;

FIG. 3 is a view similar to FIG. 2 having on both its opposite extended surfaces a cutting surface stratum of the invention, and

FIG. 4 is a table giving the composition and characteristics of different metal carbide cutting tool inserts referred to hereinafter.

The invention will be herein described in connection with examples wherein a known sintered metal carbide tool insert is provided along its cutting edge surface with a thin erosion and heat-resisting stratum containing a high proportion of one or more of carbides or borides of Ti, Zr, V, Ta or Nb or at least 50% of aluminum oxide.

iFi'IG. 1 is a curve diagram wherein the cutting eiciency, as a function of cutting speed, of a cutting tool insert of the invention containing 255% titanium carbide in its cutting surface layer when cutting steel which excretes a non-metallic deposit in comparison with that of a prior-art cutting tool insert containing 8% titanium carbide in its cutting edge surface layer. The cutting efficiency is indicated on the ordinate axis by the thickness in fmicrometers (am.) of the non-metallic inclusion deposit excreted on the cutting ed-ge surfaces for cutting velocities increasing to 350 meters per minute (m./min.). Curve 15 gives the results for a tool insert of the invention containing 25% titanium carbide in its cutting surface layer and curve 16 gives corresponding results for a cutting tool insert containing 8% titanium carbide in its cutting surface layer. Curve 15 shows that with the cutting surface layer of the invention containing 25% TiC, high cutting efficiency is secured over a wide range of desirable cutting speeds between 50 and 350 m./min. A cutting duration of 0.5 to 1.5 minutes was required for forming the thick non-metallic inclusion deposit on the cutting edge surface of such cutting tool insert of the invention.

In contrast, curve 16 shows the poor cutting efficiency of a similar cutting tool insert, containing only 8% titanium carbide in the cutting edge surface layer. As seen by curve 15 such cutting tool insert, containing only 8% TiC in the cutting edge surface could not be used for cutting speeds above m./min. because such cutting insert would be worn out by erosion faster than the build up of the inclusion deposit on its cutting edge surface.

The cutting edge surface of such cutting tool insert of the invention containing a high proportion of the erosion and heat resistant carbides or `borides of Ti, Zr, V, Ta and Nb or at least 50% A1203 exhibit brittleness when subjected to bending strains.

In accordance with the invention, known metal-carbide cutting tool inserts have afxed to its cutting edge surface a thin erosion and heat-resistant stratum containing a very high proportion of at least 15% of one or more of the above specified carbides or borides of Zr, V, Ta, Nb and Ti or at least 50% A1203. Also, such heat and erosion resisting cutting surface stratum contains at least 50% aluminum oxide. Such erosion and heat resisting cutting edge surface stratum layer have a thickness between 0.01 to 1 mm. (millimeters) and very effective results are obtained with such erosion and heat resisting cutting edge surface layer or stratum having thickness of 0.05 to 0.5 mm., and containing at least 15 of one or more of the carbides or borides of zirconium, Vanadium, tantalum, or niobium, or at least 50% aluminum oxide.

Cutting tool inserts having the high erosion and heat resistant cutting edge surface stratum containing at least 15 of the carbides or borides of Zr, V, Ta, Nb or Ti, or 50% aluminum oxide, although having only such small thickness have proven to operate over an unusually long life, even when cutting non-metallic inclusion containing steels with high velocity.

Cutting tool inserts of the invention may be made by various procedures. As an example, the known metal carbide cutting tool inserts containing principally tungsten carbide may have secured to its cutting surface the thin coating consisting of the erosion and heat resistant composition of the invention. As another example, the exterior surface stratum of the cutting tool insert containing principally tungsten carbide with only 8% titanium carbide may be enriched with such additional metal carbides or borides of Ti, Ta, Zr, Nb. This may be done by packing the tool inserts in a mass of powder particles containing such erosion and heat-resistant carbide composition ingredients and heating such powder mass to cause these pack composition ingredients to diffuse from the pack or the surrounding gas phase into the insert body. The soobtained diffusion enriched thin tool surface stratum having a thickness of about 10100 microns is sufiicient to protect the cutting edge tool surface against erosion as the non-metallic inclusion layer is deposited thereon from the steel by the cutting operation.

FIGS. 2, 2A and 3 show two known types metalcarbide cutting inserts, each formed with an interior body consisting mainly of tungsten carbide and only a small proportion of titanium and tantalum carbide. However, the cutting edge surface or surface of each such tool insert is provided with a thin erosion and heat resisting layer or stratum containing at least of one or more of the carbides or borides of Ti, Ta, Zr, V and Nb or at least 50% aluminum oxide which assure that such tool inserts are efficient in cutting steel containing non-metallic inclusion. This is due to the fact that when cutting such steels with such cutting tool inserts of the invention, such non-metallic steel occlusions deposit on such cutting edge surface a layer of these non-metallic occlusion which deposit reduces erosion of the cutting edge surface stratum lof the cutting tool insert.

In the subsequent description of the invention, the metal-carbide composition of the cutting tool inserts will be identified by the generally used designations, originally adopted by The Swedish Association of Metalworking Industries, for the different types of cutting tool inserts, which designations are used, for example, in an article Standard Machining Test which appeared in the January/February 1968 issue of Cutting Tool Engineering (including pages 26, 27 thereof). In the table in FIG. 4, the different known cutting tool inserts are designated in the first column by symbols P01 to P50, M10 to M40 and K01 to K40. The successive columns of the table give for 4 each such tool designation its composition, density, Vickers hardness, bending strength, compression strength and elastic modules. This table corresponds to that contained in the German publication by Dr. Ing. H. Beutel in Technische Mitteilungen, June 1959, pages 218-228, published by Deutsche Edelstahlwerke A.'G.

Referring to the example of FIG. 2, 2A, a cutting tool insert 20 has a main cutting body 21 of the IlSO carbide group P30 consisting essentially of 82% tungsten carbide, 8% titanium and tantalum carbide and 10% cobalt, and which main body 21 has bending strength of about kg./n1m.2 (kilogram per millimeter square), compression strength of about 500 kg./mm.2 and an elastic modulus of 56,000 kg/mm?. However, its cutting edge surface layer or stratus 22 consists essentially of one of the ISO carbide groups P01 to P10 `which has high erosion and heat resistance when cutting steel which contains nonmetallic occlusions.

The cutting edge surface layer 22 consists of approximately at most 77% tungsten carbide, 5 to 9% cobalt, and the balance at least 18% of titanium and tantalum carbide which gives this cutting edge surface stratum the higher erosion and heat resistance and assures that when the cutting insert 20 is used to cut non-metallic occlusions containing steel, it causes the steel to deposit a layer of these occlusions on the cutting edge surface stratum 22 of the cutting insert 20, thereby reducing the erosion of the insert and securing more efficient cutting action as illustrated by curves 1S and 16 of FIG. 1. As seen in the table, cutting tool inserts with the compositions of P01 and P10 have a materially lower bending and compression strength and a much lower elastic modulus than the P30 composition of the main insert body 21.

In an analogous way, the cutting tool insert of FIG. 3 has a similar main inner body 31 of the ISO group P30 and both its cutting edge surfaces consist of thin layers or strata 32, 33 made with ISO carbide groups P01 to P10 which contain at most 77% tungsten carbide and at least 18% titanium and tantalum carbide.

Cutting tool inserts of the type described in connection with FIGS. 2, 2A and 3 may be produced by any known method used in making tungsten carbide tool inserts. As an example, a tool insert of the P30 type may be packed in a powder mixture of titanium containing ingredients so that upon heating suiiiciently there is a diffusion of titanium into the surface stratum and formation thereon of 10 to 100 micron thick which contains at least 15% titanium carbide. Such cutting tool insert will be Very eicient in cutting steels which contain non-metallic inclusions because these occlusions will form a surface deposit on the titanium carbide enriched surface layer and reduce erosion thereof.

Cutting tool inserts having a thicker erosion and heat resisting layer or layers-such as shown in FIGS. 2 to 3 along its cutting edge surface, may be produced by known metallurgy processes. Into a known type of die cavity used to make known cutting tool inserts, such as shown in FIGS. 2, 2A, is first filled `with the contents of P30 carbide composition of a thickness corresponding to main carbide body 21, over which is deposited a thin layer or stratum of the P01.4 carbide composition. Thereafter, the composite powder filling is treated and sintered in the same way as in the production of the known P01.2 to P50 inserts of the table in FIG. 4 to yield the cutting tool of FIGS. 2, 2A. In an analogous way the cutting tool insert of FIG. 3 is produced by first depositing in the die cavity a thin layer or stratum of the carbide composition P011 followed by the thick layer of composition P30 followed by a thin layer of the P01.2 composition, and thereafter treated in the same way to yield the cutting tool insert of FIG. 3.

Below are given further examples of cutting tool inserts of the invention.

EXAMPLE 2 A finished cutting tool insert of composition P30 (of medium hardness and high toughness, consisting approximately of 5% TiC, 3% tantalum-niobium carbide, 10% cobalt, and with balance tungsten carbide) its cutting edge surface is given the final polish. This cutting tool insert was packed in a mixture of powder particles consisting of 90% titanium oxide TiO2 and 10% graphite, and the pack of the insert is heated for one hour at 1350 C. This treatment yields a cutting tool insert having the original composition along the stratum of its polished edge surface enriched with titanium carbide and corresponding to the carbide composition P of FIG. 4, containing about 28% titanium carbide. Such cutting tool insert proved efficient in cutting non-metallic inclusion containing sheets of 75 kg./rnm.2 strength with cutting surface with lifetime up to 180 minutes.

EXAMPLE 3 A finished cutting tool insert of the same composition P30 (as in Example 2) was heated in a vacuum to 1250 C., and thereafter subjected at such temperature to a gas mixture consisting of 40 vol. percent TiCl4 and 60* vol. percent CH., for 40 minutes (vol. percent means volume percent). After this treatment, the polished surface cutting of the insert had micron thick surface layer or stratum of titanium carbide which was firmly anchored to and constituted an integral part of the cutting insert. The subsequent test of cutting non-metallic inclusion containing steel at 75 kg./mm.2 strength, proved this cutting tool insert efficient cutting steel as if its cutting edge surface layer consisted of the above identified titanium rich composition. It cut such steel and formed a non-metallic deposit on its cutting surfaces over a speed range of 160 to 250 m./min. with lifetime up to 180 minutes.

EXAMPLE 4 A cutting insert plate was produced with a die cavity by first depositing therein a thin powder mixture stratum of 1.5 mm. thickness consisting of 20% titanium carbide, 20% tantalum carbide and as balance tungsten carbide. Over this thin first stratum was deposited a 7 mm. thick layer of a powder mixture consisting of tungsten carbide and 8% cobalt. Over this thick powder mixture layer was deposited another similar 1.5 mm. thin stratum of the same composition as the first 1.5 mm. thin stratum. The powder particle size is between 1 to 5 microns. After compression, the composite powder mixture layer and strata was 1.6 tons/cm.2 (tons per centimeter square) the resulting compact had been subjected to sintering treatments such as at 1430 C. for one hour, such as applied to known cutting inserts of this type. The resulting cutting insert consisted of a thick main body (such as 31 in FIG. 3) of tough carbide composition K30 having along each of its opposite surfaces 0.6 mm. thin cutting edge surfaces, layer or strata 32, 33 of a carbide composition P10. Inclusion containing steel was cut with such cutting edge surfaces while excreting a non-metallic deposit on the cutting edge surface with speeds of 160 to 200 m./min., a cutting-cross-section of 2 mm. x 0.3 mm. and lifetime of about 150 minutes.

EXAMPLE 5 Within a graphite mold die cavity of a cutting insert was first deposited a 1.5 mm. thin stratum of a powder stratum of the same composition as the first stratum. The powder particles should be of 2 to 6 microns particle size. After hot pressing at about 1400 C. with about kg./cm.2 for about 2 to 4 minutes pressure, there was obtained a cutting insert plate containing a main plate body consisting of the carbide composition P-20 having along its opposite cutting edge surfaces about 0.5 mm. thin strata containing about 94% titanium carbide and tantalum carbide. Inclusion containing steel was etliciently cut with these cutting edge surfaces while excreting thereon an inclusion deposit with speeds of to 300 m./min. A lifetime up to 150 minutes was reached.

EXAMPLE 6 m./min. and lifetime of minutes could be reached.

It should be noted that the erosion and heat resistant cutting edge surface layer containing at least 15% of the carbides or borides of Ti, Ta, Zr, Nb and V, may contain as balance one or more of the carbides of tungsten or molybdenum or chromium and the main body of such inserts may be formed of such carbides.

The described examples of the invention will suggest various modifications and the claims should not be limited to these examples.

We claim:

1. A cutting tool insert comprising a relatively thick body layer containing a large proportion of tungsten carbide and having along its cutting edge surface, a stratum of 0.01 to l millimeter thick containing at least 15% of one or more of the further carbides or borides of titanium, tantalum, zirconium, niobium or vanadium for providing increased cutting efficiency over a range of desirable cutting speeds as compared to the efficiency exhibited by said body layer alone;

said cutting edge surface stratum of said cutting tool having been enriched with one or more of said further carbides by didusion.

2. A cutting tool insert for shaping a deposit-forming steel structure containing inclusions comprising a relatively thick body layer containing a large proportion of tungsten carbide and having along its cutting edge surface, a stratum of 0.01 to l millimeter thick containing at least 15 of one or more of the further carbides or borides of titanium, tantalum, zirconium, niobium or vanadium which cause deposition of a layer of such inclusion on said cutting edge surface when cutting said steel structure, for providing increased cutting efficiency over a range of desirable cutting speeds as compared to the efficiency exhibited by said body layer alone;

said cutting edge surface stratum of said cutting tool having been enriched with one or more of said further carbides by diffusion.

References Cited UNITED STATES PATE- TS 2,053,977 9/ 1936 Taylor 29-95 2,414,231 1/ 1947 Kraus 29-95 1,973,425 9/ 1934 Comstock 2995X HARRISON L. HINSON, Primary Examiner UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3.564,683 Dated February 23. 1971 .Invento(s) wolfgang SChedler et al It is certified that error appears in the Yabove-identified patent and that said Letters Patent are hereby corrected es show-n below:

column 1,V line 19 3'35" shou1d read: 350' Column 6 line 18, delete "15% ttanum carbide,"

Slgned` and sealed this 21th iay4 of July 1972.

(SEAL) Attest:

ROBERT GOTTSCHALK EDWARD IJI.FLE1CIIER,JR.

Commissioner of Pater.

Attestinf; Officer 

